1. Field of Invention
This invention relates to a digital display clock for motor vehicles and in particular to digital type clock for motor vehicles which utilizes luminescent elements with large electric current consumption as the time display.
2. Description of the Prior Art
Since vehicle passengers must be able to read the time quickly and easily while driving a motor vehicle, a digital type display clock finds particular utility. The digital display clock for motor vehicles works such that the display section receives time signals from means for generating time signals. Among the various elements available for the digital time display section, such as luminescent diodes, fluorescent display tubes, liquid crystals, etc., the luminescent diodes and the fluorescent display tubes have excellent characteristics such as emission of visible light through the excitation luminescence action, strong brightness for easy reading, etc., when compared with non self-luminescent elements, liquid crystals, for example. However, the self-luminescent type digital element mainly falls into a luminescent element category of the current drive type, and requires very large electric current comsumption for continuous display action. In particular, since electrical power for a clock for a motor vehicle is always supplied by the battery, which is maintained in good capacity through the charging action at a motor vehicle in operation, large electric current consumption when the engine is not running causes an objectionable drain of the battery.
A typical conventional digital display clock for motor vehicle is equipped with clock driving section wherein electric current is always supplied, and with digital time display section wherein electric current supply is controlled by a switch interlocked to the ignition switch. The digital time display action can be obtained only when the motor vehicle is in operation. The increase of electric current consumption is thus prevented. Furthermore, the prior art circuit has another drawback in that troublesome ignition key switching is always required to read the time when parking the motor vehicle. In particular, one staying in the motor vehicle is unable to know the time without an ignition key, and it is extremely dangerous for the one without driving competance of motor vehicles to switch on the ignition switch in order to try to read the time.